SUBUNIT ORGANIZATION AND STRUCTURE OF LON PROTEASE

扫描透射电子显微镜（STEM）已被应用于确定ATP依赖性蛋白酶，Lon的亚基组织。这种酶在原核生物以及真核生物的线粒体中降解错误折叠的蛋白质中起重要作用。Lon由含有ATP酶（A）和蛋白酶（P）结构域的单个多肽链的多个拷贝组成。细菌Lon的序列与真核生物Lon的序列有很强的同源性，真核生物Lon已被报道形成七聚体环。然而，对于细菌Lon，目前公布的数据是不确定的。暗场STEM测量显示全长E. coli Lon（野生型和ser-ala突变体）以及Lon-NA由十二聚体组成，而Lon-AP形成六聚体。通过与作为ClpAP蛋白酶复合物的ATP酶组分的蛋白ClpA类比，Lon可能由两个六聚体环组成。Lon-AP仅形成六聚体的事实表明，N-末端结构域可能是全酶中两个六聚体环缔合所必需的。- 扫描透射电镜，lon蛋白酶，亚基组织，结构，分子量

Scanning transmission electron microscopy (STEM) has been applied to determine the subunit organization of the ATP-dependent protease, Lon. This enzyme plays an important role in degrading misfolded proteins in prokaryotes as well as in the mitochrondria of eukaryotes. Lon consists of multiple copies of a single polypeptide chain that contains both the ATPase (A) and protease (P) domains. The sequence of bacterial Lon has a strong homology with eukaryotic Lon which has been reported to form heptameric rings. However, for bacterial Lon, currently published data are inconclusive. Dark-field STEM measurements show that full-length E. coli Lon (wild type and a ser-ala mutant) as well as Lon-NA are composed of dodecamers, whereas Lon-AP forms hexamers. By analogy with the protein ClpA which is the ATPase component of the ClpAP protease complex, it is likely that Lon is comprised of two hexameric rings. The fact that Lon-AP only forms hexamers suggests that the N-terminal domain may be required for association of two hexameric rings in the holoenzyme. - Scanning transmission electron microscopy, lon protease, subunit organization, structure, molecular weight